1. Field of the Invention
The present invention relates to a method for forming a shallow trench isolation (STI). In particular, the present invention relates to a method for forming an STI with ideal height of a liner.
2. Description of the Prior Art
As known by persons of ordinary skills in the art, the uniform control of the height of the silicon nitride liner in the STI structure is essential to the formation of the corner device. However, the current dry etching method is not ideal for forming the silicon nitride liner of uniform height.
If the level of the silicon nitride liner is too high after the etching, the high-density plasma would usually fail to fill the trench with an oxide and therefore voids appear.
On the other hand, if the level of the silicon nitride liner is too low, the spin-on-glass (SOG) layer in the trench will suffer the loss of its protection and is likely to be damaged by the following wet etching procedure. Neither outcome is desirable. Accordingly, a novel method is needed to form an STI with a liner of uniform and ideal height.